Fix styles

- Slightly update the red color of top bar's "buy tickets" button to match the hero header
- Speakers avatars grid was broken for medium and small screens.

After:
![screen shot 2014-04-20 at 18 22 57](https://cloud.githubusercontent.com/assets/224928/2750970/93fa512e-c8a8-11e3-80a8-0ea263fc3491.png)

Before:
![screen shot 2014-04-20 at 18 22 48](https://cloud.githubusercontent.com/assets/224928/2750971/9553767c-c8a8-11e3-9803-1e2b4f794347.png)